Broadcast概述
该部分内容主要翻译自Google Android Developers文档
Android Broadcast机制采用类似发布/订阅设计模式，应用可以注册接收特定的广播，
当广播发出时，系统自动向订阅改广播的的接收者发送。
系统广播
只能由系统发送的广播, 当某些系统事件发生时，会发出系统广播，比如（android.intent.action.AIRPLANE_MODE）.
完整的系统广播列表可以查看sdk/platforms/android-xx/data下的BROADCAST_ACTIONS.TXT
系统广播的变化
Android 7.0不再发送以下系统广播，
- ACTION_NEW_PICTURE
- ACTION_NEW_VIDEO
运行在Android 7.0(API 24)及以上的设备，注册下面的广播必须使用registerReceiver，在AndroidManifest中定义一个receiver将不工作。
- CONNECTIVITY_ACTION
注册广播接收机
AndroidManifest中定义receiver
- 子类化BroadcastReceiver，同时实现onReceive方法
public class ManifestReceiver extends BroadcastReceiver {
private static final String LOG_TAG = ManifestReceiver.class.getSimpleName();
@Override
public void onReceive(Context context, Intent intent) {
Log.i(LOG_TAG, "onReceive " + intent.getAction());
}
}
- 在AndroidManifest中添加<receiver>元素
<receiver android:name=".ManifestReceiver">
<intent-filter>
<action android:name="android.intent.action.BOOT_COMPLETED" />
<action android:name="android.intent.action.BATTERY_CHANGED" />
</intent-filter>
</receiver>
当收到广播的时候，系统会创建一个新的BroadcastReceiver组件来处理它，广播接收机对象仅仅在调用onReceive方法期间有效，一旦onReceive返回，系统就可能回收改组件。
context中注册receiver
- 创建BroadcastReceiver和IntentFilter的实例，使用registerReceiver注册
public class ContextReceiver extends BroadcastReceiver {
private static final String LOG_TAG = ContextReceiver.class.getSimpleName();
@Override
public void onReceive(Context context, Intent intent) {
Log.i(LOG_TAG, "onReceive " + intent.getAction());
}
}
registerReceiver(new ContextReceiver(), new IntentFilter(Intent.ACTION_AIRPLANE_MODE_CHANGED));
注册本地广播，使用
LocalBroadcastManager.registerReceiver(BroadcastReceiver, IntentFilter)代替
- 停止接受广播，调用
unregisterReceiver(android.content.BroadcastReceiver)，当不再需要或者Context不可用时，确保注销广播接收机。
registerReceiver与unregisterReceiver应成对出现，例如，在Activity的onCreate中注册，应该在onDestory中注销；在onResume中注册，则应该在onPause中注销，不要再onSaveInstanceState中注销广播接收机。
广播接收机对进程状态的影响
广播接收机的状态影响其宿主进程的状态。例如，当宿主进程正在执行广播接收机的onReceive是，它是一个前台进程，除非在紧急情况下，否则系统一般不会杀它。一旦宿主进程从onReceive中返回，如果没有其他组件的话，系统为了回收资源可能会杀掉该进程。由于这个原因，不要在广播接收机的onReceive中启动长期运行的后台线程。为了避免这个问题，应该使用goAsync()或者使用JobScheduler。
下面是使用goAsync()的例子
public void onReceive(Context context, final Intent intent) {
final PendingResult pendingResult = goAsync();
AsyncTask<String, Integer, String> asyncTask = new AsyncTask<String, Integer, String>() {
@Override
protected String doInBackground(String... strings) {
StringBuilder sb = new StringBuilder();
sb.append("Action " + intent.getAction() + "\n");
sb.append("Uri " + intent.toUri(Intent.URI_INTENT_SCHEME) + "\n");
Log.i(LOG_TAG, sb.toString());
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
pendingResult.finish();
return null;
}
};
asyncTask.execute();
}
对于goAsync()以及JobScheduler的实现原理，我们后续讨论。
发送广播
-
sendOrderedBroadcast(Intent, String)发送有序广播 -
sendBroadcast(Intent)发送普通广播 -
LocalBroadcastManager.sendBroadcast用于发送发送者和接收者在同一app内的广播，更加高效，无
需跨进程通信
限制广播的权限
发送带有权限的广播
当我们调用sendBroadcast(Intent)或者sendOrderedBroadcast(Intent, String)发送广播时，可以添加权限参数，这样只有申请了相应权限的广播接收机才能收到广播。例如，我们使用如下代码发送广播：
sendBroadcast(new Intent("com.example.NOTIFY"),
Manifest.permission.SEND_SMS);
接收者必须申请权限才能接受广播
<uses-permission android:name="android.permission.SEND_SMS"/>
带有权限的广播接收机
如果注册广播接收机的时候添加特定的权限参数，那么只有申请了相应权限的发送者才能发送广播到接收机。
例如广播接收机添加如下权限
<receiver android:name=".ManifestReceiver"
android:permission="android.permission.SEND_SMS">
<intent-filter>
<action android:name="android.intent.action.BOOT_COMPLETED" />
<action android:name="android.intent.action.BATTERY_CHANGED" />
</intent-filter>
</receiver>
IntentFilter filter = new IntentFilter(Intent.ACTION_AIRPLANE_MODE_CHANGED);
registerReceiver(receiver, filter, Manifest.permission.SEND_SMS, null );
为了能发送广播到上面的广播接收机，发送app应该申请如下权限
<uses-permission android:name="android.permission.SEND_SMS"/>
注册广播接收机的流程分析（以context注册为例）
下面从registerReceiver开始分析
@Override
public Intent registerReceiver(BroadcastReceiver receiver, IntentFilter filter) {
return registerReceiver(receiver, filter, null, null);
}
- receiver：需要注册的广播接收机
- filter：用于过滤接收的广播
registerReceiver最终调用registerReceiverInternal，下面分析registerReceiverInternal。
private Intent registerReceiverInternal(BroadcastReceiver receiver, int userId,
IntentFilter filter, String broadcastPermission,
Handler scheduler, Context context) {
IIntentReceiver rd = null;
if (receiver != null) {
if (mPackageInfo != null && context != null) {
// scheduler为广播处理handler,默认为UI Thread的handler
if (scheduler == null) {
scheduler = mMainThread.getHandler();
}
// 创建ReceiverDispathcer以及IIntentReceiver.Stub对象用于接收分发广播
rd = mPackageInfo.getReceiverDispatcher(
receiver, context, scheduler,
mMainThread.getInstrumentation(), true);
} else {
if (scheduler == null) {
scheduler = mMainThread.getHandler();
}
rd = new LoadedApk.ReceiverDispatcher(
receiver, context, scheduler, null, true).getIIntentReceiver();
}
}
try {
// 通过Binder IPC向AMS注册广播接收机
final Intent intent = ActivityManagerNative.getDefault().registerReceiver(
mMainThread.getApplicationThread(), mBasePackageName,
rd, filter, broadcastPermission, userId);
if (intent != null) {
intent.setExtrasClassLoader(getClassLoader());
intent.prepareToEnterProcess();
}
return intent;
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
ReceiverDispatcher以及IIntentReceiver对于广播的分发比较关键。
- ReceiverDispatcher持有IIntentReceiver.Stub对象的引用
- BroadcastReceiver与ReceiverDispatcher一一对应，存放于ArrayMap中
下面分析ActivityManagerService中registerReceiver的实现。
public Intent registerReceiver(IApplicationThread caller, String callerPackage,
IIntentReceiver receiver, IntentFilter filter, String permission, int userId) {
enforceNotIsolatedCaller("registerReceiver");
ArrayList<Intent> stickyIntents = null;
ProcessRecord callerApp = null;
int callingUid;
int callingPid;
synchronized(this) {
if (caller != null) {
// 获取调用者的进程记录
callerApp = getRecordForAppLocked(caller);
if (callerApp == null) {
throw new SecurityException(
"Unable to find app for caller " + caller
+ " (pid=" + Binder.getCallingPid()
+ ") when registering receiver " + receiver);
}
if (callerApp.info.uid != Process.SYSTEM_UID &&
!callerApp.pkgList.containsKey(callerPackage) &&
!"android".equals(callerPackage)) {
throw new SecurityException("Given caller package " + callerPackage
+ " is not running in process " + callerApp);
}
callingUid = callerApp.info.uid;
callingPid = callerApp.pid;
} else {
callerPackage = null;
callingUid = Binder.getCallingUid();
callingPid = Binder.getCallingPid();
}
// 通常userId为0，检查广播userId权限
userId = mUserController.handleIncomingUser(callingPid, callingUid, userId, true,
ALLOW_FULL_ONLY, "registerReceiver", callerPackage);
Iterator<String> actions = filter.actionsIterator();
if (actions == null) {
ArrayList<String> noAction = new ArrayList<String>(1);
noAction.add(null);
actions = noAction.iterator();
}
// Collect stickies of users
// 收集对应于该actions的粘性广播intent
int[] userIds = { UserHandle.USER_ALL, UserHandle.getUserId(callingUid) };
while (actions.hasNext()) {
String action = actions.next();
for (int id : userIds) {
ArrayMap<String, ArrayList<Intent>> stickies = mStickyBroadcasts.get(id);
if (stickies != null) {
ArrayList<Intent> intents = stickies.get(action);
if (intents != null) {
if (stickyIntents == null) {
stickyIntents = new ArrayList<Intent>();
}
stickyIntents.addAll(intents);
}
}
}
}
}
ArrayList<Intent> allSticky = null;
if (stickyIntents != null) {
final ContentResolver resolver = mContext.getContentResolver();
// Look for any matching sticky broadcasts...
for (int i = 0, N = stickyIntents.size(); i < N; i++) {
Intent intent = stickyIntents.get(i);
// If intent has scheme "content", it will need to acccess
// provider that needs to lock mProviderMap in ActivityThread
// and also it may need to wait application response, so we
// cannot lock ActivityManagerService here.
if (filter.match(resolver, intent, true, TAG) >= 0) {
if (allSticky == null) {
allSticky = new ArrayList<Intent>();
}
allSticky.add(intent);
}
}
}
// 返回第一个intent
// The first sticky in the list is returned directly back to the client.
Intent sticky = allSticky != null ? allSticky.get(0) : null;
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST, "Register receiver " + filter + ": " + sticky);
if (receiver == null) {
return sticky;
}
synchronized (this) {
if (callerApp != null && (callerApp.thread == null
|| callerApp.thread.asBinder() != caller.asBinder())) {
// Original caller already died
return null;
}
// receiver.asBinder()返回BinderProxy对象
// ReceiverList表示一个接收一个或多个广播的接收机对象
ReceiverList rl = mRegisteredReceivers.get(receiver.asBinder());
if (rl == null) {
rl = new ReceiverList(this, callerApp, callingPid, callingUid,
userId, receiver);
if (rl.app != null) {
rl.app.receivers.add(rl);
} else {
try {
// ReceiverList接收Binder(InnerReceiver)死亡通知
receiver.asBinder().linkToDeath(rl, 0);
} catch (RemoteException e) {
return sticky;
}
rl.linkedToDeath = true;
}
// 保存ReceiverList
mRegisteredReceivers.put(receiver.asBinder(), rl);
} else if (rl.uid != callingUid) {
throw new IllegalArgumentException(
"Receiver requested to register for uid " + callingUid
+ " was previously registered for uid " + rl.uid);
} else if (rl.pid != callingPid) {
throw new IllegalArgumentException(
"Receiver requested to register for pid " + callingPid
+ " was previously registered for pid " + rl.pid);
} else if (rl.userId != userId) {
throw new IllegalArgumentException(
"Receiver requested to register for user " + userId
+ " was previously registered for user " + rl.userId);
}
BroadcastFilter bf = new BroadcastFilter(filter, rl, callerPackage,
permission, callingUid, userId);
// BroadcastFilter添加到ReceiverList
rl.add(bf);
if (!bf.debugCheck()) {
Slog.w(TAG, "==> For Dynamic broadcast");
}
// BroadcastFilter添加到mReceiverResolver
mReceiverResolver.addFilter(bf);
// Enqueue broadcasts for all existing stickies that match
// this filter.
// 向新注册的接收机发送粘性广播
if (allSticky != null) {
ArrayList receivers = new ArrayList();
receivers.add(bf);
final int stickyCount = allSticky.size();
for (int i = 0; i < stickyCount; i++) {
Intent intent = allSticky.get(i);
BroadcastQueue queue = broadcastQueueForIntent(intent);
BroadcastRecord r = new BroadcastRecord(queue, intent, null,
null, -1, -1, null, null, AppOpsManager.OP_NONE, null, receivers,
null, 0, null, null, false, true, true, -1);
queue.enqueueParallelBroadcastLocked(r);
queue.scheduleBroadcastsLocked();
}
}
return sticky;
}
}
对于接收粘性广播的接收机，注册完成，便可收到广播。
发送普通（有序）广播的流程分析
下面从sendBroadcast开始分析
public void sendBroadcast(Intent intent, String receiverPermission) {
warnIfCallingFromSystemProcess();
String resolvedType = intent.resolveTypeIfNeeded(getContentResolver());
String[] receiverPermissions = receiverPermission == null ? null
: new String[] {receiverPermission};
try {
intent.prepareToLeaveProcess(this);
调用同步的Binder IPC请求发送广播
ActivityManagerNative.getDefault().broadcastIntent(
mMainThread.getApplicationThread(), intent, resolvedType, null,
Activity.RESULT_OK, null, null, receiverPermissions, AppOpsManager.OP_NONE,
null, false, false, getUserId());
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
下面看broadcastIntent
public final int broadcastIntent(IApplicationThread caller,
Intent intent, String resolvedType, IIntentReceiver resultTo,
int resultCode, String resultData, Bundle resultExtras,
String[] requiredPermissions, int appOp, Bundle bOptions,
boolean serialized, boolean sticky, int userId) {
enforceNotIsolatedCaller("broadcastIntent");
synchronized(this) {
// 检查可能的文件描述符泄露以及是否允许在系统启动完成之前发送广播
intent = verifyBroadcastLocked(intent);
final ProcessRecord callerApp = getRecordForAppLocked(caller);
final int callingPid = Binder.getCallingPid();
final int callingUid = Binder.getCallingUid();
final long origId = Binder.clearCallingIdentity();
int res = broadcastIntentLocked(callerApp,
callerApp != null ? callerApp.info.packageName : null,
intent, resolvedType, resultTo, resultCode, resultData, resultExtras,
requiredPermissions, appOp, bOptions, serialized, sticky,
callingPid, callingUid, userId);
Binder.restoreCallingIdentity(origId);
return res;
}
}
下面分析broadcastIntentLocked
final int broadcastIntentLocked(ProcessRecord callerApp,
String callerPackage, Intent intent, String resolvedType,
IIntentReceiver resultTo, int resultCode, String resultData,
Bundle resultExtras, String[] requiredPermissions, int appOp, Bundle bOptions,
boolean ordered, boolean sticky, int callingPid, int callingUid, int userId) {
intent = new Intent(intent);
// By default broadcasts do not go to stopped apps.
// 对于正在停止的package，不发送广播
intent.addFlags(Intent.FLAG_EXCLUDE_STOPPED_PACKAGES);
// If we have not finished booting, don't allow this to launch new processes.
// 系统还没有启动完成，只发送给宿主进程已经运行的广播接收机
if (!mProcessesReady && (intent.getFlags()&Intent.FLAG_RECEIVER_BOOT_UPGRADE) == 0) {
intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY);
}
if (DEBUG_BROADCAST_LIGHT) Slog.v(TAG_BROADCAST,
(sticky ? "Broadcast sticky: ": "Broadcast: ") + intent
+ " ordered=" + ordered + " userid=" + userId);
if ((resultTo != null) && !ordered) {
Slog.w(TAG, "Broadcast " + intent + " not ordered but result callback requested!");
}
// 广播接收者的userId
userId = mUserController.handleIncomingUser(callingPid, callingUid, userId, true,
ALLOW_NON_FULL, "broadcast", callerPackage);
......
// Verify that protected broadcasts are only being sent by system code,
// and that system code is only sending protected broadcasts.
// 保护性广播只能由系统发送
final String action = intent.getAction();
final boolean isProtectedBroadcast;
try {
isProtectedBroadcast = AppGlobals.getPackageManager().isProtectedBroadcast(action);
} catch (RemoteException e) {
Slog.w(TAG, "Remote exception", e);
return ActivityManager.BROADCAST_SUCCESS;
}
final boolean isCallerSystem;
// 判定广播发送者是否为system
switch (UserHandle.getAppId(callingUid)) {
case Process.ROOT_UID:
case Process.SYSTEM_UID:
case Process.PHONE_UID:
case Process.BLUETOOTH_UID:
case Process.NFC_UID:
isCallerSystem = true;
break;
default:
isCallerSystem = (callerApp != null) && callerApp.persistent;
break;
}
......
// Add to the sticky list if requested.
// 正在发送的广播是粘性广播
if (sticky) {
if (checkPermission(android.Manifest.permission.BROADCAST_STICKY,
callingPid, callingUid)
!= PackageManager.PERMISSION_GRANTED) {
String msg = "Permission Denial: broadcastIntent() requesting a sticky broadcast from pid="
+ callingPid + ", uid=" + callingUid
+ " requires " + android.Manifest.permission.BROADCAST_STICKY;
Slog.w(TAG, msg);
throw new SecurityException(msg);
}
if (requiredPermissions != null && requiredPermissions.length > 0) {
Slog.w(TAG, "Can't broadcast sticky intent " + intent
+ " and enforce permissions " + Arrays.toString(requiredPermissions));
return ActivityManager.BROADCAST_STICKY_CANT_HAVE_PERMISSION;
}
if (intent.getComponent() != null) {
throw new SecurityException(
"Sticky broadcasts can't target a specific component");
}
// We use userId directly here, since the "all" target is maintained
// as a separate set of sticky broadcasts.
if (userId != UserHandle.USER_ALL) {
// But first, if this is not a broadcast to all users, then
// make sure it doesn't conflict with an existing broadcast to
// all users.
// 如果当前的粘性广播不是发送给all users，检查是否冲突
ArrayMap<String, ArrayList<Intent>> stickies = mStickyBroadcasts.get(
UserHandle.USER_ALL);
if (stickies != null) {
ArrayList<Intent> list = stickies.get(intent.getAction());
if (list != null) {
int N = list.size();
int i;
for (i=0; i<N; i++) {
if (intent.filterEquals(list.get(i))) {
throw new IllegalArgumentException(
"Sticky broadcast " + intent + " for user "
+ userId + " conflicts with existing global broadcast");
}
}
}
}
}
// 将粘性广播添加到接收用户对应的ArrayMap中
ArrayMap<String, ArrayList<Intent>> stickies = mStickyBroadcasts.get(userId);
if (stickies == null) {
stickies = new ArrayMap<>();
mStickyBroadcasts.put(userId, stickies);
}
ArrayList<Intent> list = stickies.get(intent.getAction());
if (list == null) {
list = new ArrayList<>();
stickies.put(intent.getAction(), list);
}
final int stickiesCount = list.size();
int i;
for (i = 0; i < stickiesCount; i++) {
if (intent.filterEquals(list.get(i))) {
// This sticky already exists, replace it.
list.set(i, new Intent(intent));
break;
}
}
if (i >= stickiesCount) {
list.add(new Intent(intent));
}
}
int[] users;
// 广播接收用户
if (userId == UserHandle.USER_ALL) {
// Caller wants broadcast to go to all started users.
users = mUserController.getStartedUserArrayLocked();
} else {
// Caller wants broadcast to go to one specific user.
users = new int[] {userId};
}
// Figure out who all will receive this broadcast.
List receivers = null;
List<BroadcastFilter> registeredReceivers = null;
// Need to resolve the intent to interested receivers...
if ((intent.getFlags()&Intent.FLAG_RECEIVER_REGISTERED_ONLY)
== 0) {
// 需要收集静态广播接收机，查找接收该intent的静态广播接收机
receivers = collectReceiverComponents(intent, resolvedType, callingUid, users);
}
if (intent.getComponent() == null) {
if (userId == UserHandle.USER_ALL && callingUid == Process.SHELL_UID) {
// Query one target user at a time, excluding shell-restricted users
for (int i = 0; i < users.length; i++) {
if (mUserController.hasUserRestriction(
UserManager.DISALLOW_DEBUGGING_FEATURES, users[i])) {
continue;
}
List<BroadcastFilter> registeredReceiversForUser =
mReceiverResolver.queryIntent(intent,
resolvedType, false, users[i]);
if (registeredReceivers == null) {
registeredReceivers = registeredReceiversForUser;
} else if (registeredReceiversForUser != null) {
registeredReceivers.addAll(registeredReceiversForUser);
}
}
} else {
// 查找接收intent的动态广播接收机
registeredReceivers = mReceiverResolver.queryIntent(intent,
resolvedType, false, userId);
}
}
......
int NR = registeredReceivers != null ? registeredReceivers.size() : 0;
// 一个广播可能对应两个BroadcastRecord
if (!ordered && NR > 0) {
// If we are not serializing this broadcast, then send the
// registered receivers separately so they don't wait for the
// components to be launched.
// 并行发送普通广播给动态注册的广播接收机
// 前台广播通过前台广播队列发送，否则通过后台广播队列发送
final BroadcastQueue queue = broadcastQueueForIntent(intent);
BroadcastRecord r = new BroadcastRecord(queue, intent, callerApp,
callerPackage, callingPid, callingUid, resolvedType, requiredPermissions,
appOp, brOptions, registeredReceivers, resultTo, resultCode, resultData,
resultExtras, ordered, sticky, false, userId);
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST, "Enqueueing parallel broadcast " + r);
final boolean replaced = replacePending && queue.replaceParallelBroadcastLocked(r);
if (!replaced) {
// 广播放入(前台\后台)队列
queue.enqueueParallelBroadcastLocked(r);
queue.scheduleBroadcastsLocked();
}
registeredReceivers = null;
NR = 0;
}
// Merge into one list.
// 串行发送广播：
// 1) 普通广播发送给静态注册的广播接收机
// 2) 有序广播
int ir = 0;
if (receivers != null) {
// A special case for PACKAGE_ADDED: do not allow the package
// being added to see this broadcast. This prevents them from
// using this as a back door to get run as soon as they are
// installed. Maybe in the future we want to have a special install
// broadcast or such for apps, but we'd like to deliberately make
// this decision.
// 跳过想新安装的应用发送下面的广播，防止其安装后马上执行
String skipPackages[] = null;
if (Intent.ACTION_PACKAGE_ADDED.equals(intent.getAction())
|| Intent.ACTION_PACKAGE_RESTARTED.equals(intent.getAction())
|| Intent.ACTION_PACKAGE_DATA_CLEARED.equals(intent.getAction())) {
Uri data = intent.getData();
if (data != null) {
String pkgName = data.getSchemeSpecificPart();
if (pkgName != null) {
skipPackages = new String[] { pkgName };
}
}
} else if (Intent.ACTION_EXTERNAL_APPLICATIONS_AVAILABLE.equals(intent.getAction())) {
skipPackages = intent.getStringArrayExtra(Intent.EXTRA_CHANGED_PACKAGE_LIST);
}
......
int NT = receivers != null ? receivers.size() : 0;
int it = 0;
ResolveInfo curt = null;
BroadcastFilter curr = null;
// 将动态注册的广播接收机与静态注册的广播接收机
// 按照优先级从高到低合并到receviers中
while (it < NT && ir < NR) {
if (curt == null) {
curt = (ResolveInfo)receivers.get(it);
}
if (curr == null) {
curr = registeredReceivers.get(ir);
}
if (curr.getPriority() >= curt.priority) {
// Insert this broadcast record into the final list.
receivers.add(it, curr);
ir++;
curr = null;
it++;
NT++;
} else {
// Skip to the next ResolveInfo in the final list.
it++;
curt = null;
}
}
}
......
if ((receivers != null && receivers.size() > 0)
|| resultTo != null) {
BroadcastQueue queue = broadcastQueueForIntent(intent);
BroadcastRecord r = new BroadcastRecord(queue, intent, callerApp,
callerPackage, callingPid, callingUid, resolvedType,
requiredPermissions, appOp, brOptions, receivers, resultTo, resultCode,
resultData, resultExtras, ordered, sticky, false, userId);
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST, "Enqueueing ordered broadcast " + r
+ ": prev had " + queue.mOrderedBroadcasts.size());
if (DEBUG_BROADCAST) Slog.i(TAG_BROADCAST,
"Enqueueing broadcast " + r.intent.getAction());
// 串行发送广播
boolean replaced = replacePending && queue.replaceOrderedBroadcastLocked(r);
if (!replaced) {
queue.enqueueOrderedBroadcastLocked(r);
queue.scheduleBroadcastsLocked();
}
} else {
// There was nobody interested in the broadcast, but we still want to record
// that it happened.
if (intent.getComponent() == null && intent.getPackage() == null
&& (intent.getFlags()&Intent.FLAG_RECEIVER_REGISTERED_ONLY) == 0) {
// This was an implicit broadcast... let's record it for posterity.
addBroadcastStatLocked(intent.getAction(), callerPackage, 0, 0, 0);
}
}
return ActivityManager.BROADCAST_SUCCESS;
}
无论是并行广播还是串行广播都是通过scheduleBroadcastsLocked发送，scheduleBroadcastsLocked只是简单的发送BROADCAST_INTENT_MSG消息，在BROADCAST_INTENT_MSG消息的处理中调用processNextBroadcast()发送广播，下面看processNextBroadcast()。
final void processNextBroadcast(boolean fromMsg) {
synchronized(mService) {
BroadcastRecord r;
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST, "processNextBroadcast ["
+ mQueueName + "]: "
+ mParallelBroadcasts.size() + " broadcasts, "
+ mOrderedBroadcasts.size() + " ordered broadcasts");
mService.updateCpuStats();
if (fromMsg) {
mBroadcastsScheduled = false;
}
// First, deliver any non-serialized broadcasts right away.
while (mParallelBroadcasts.size() > 0) {
// 从mParallelBroadcasts中取出第一个BroadcastRecord
r = mParallelBroadcasts.remove(0);
r.dispatchTime = SystemClock.uptimeMillis();
r.dispatchClockTime = System.currentTimeMillis();
final int N = r.receivers.size();
if (DEBUG_BROADCAST_LIGHT) Slog.v(TAG_BROADCAST, "Processing parallel broadcast ["
+ mQueueName + "] " + r);
for (int i=0; i<N; i++) {
// 向当前广播的接收者发送
Object target = r.receivers.get(i);
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST,
"Delivering non-ordered on [" + mQueueName + "] to registered "
+ target + ": " + r);
deliverToRegisteredReceiverLocked(r, (BroadcastFilter)target, false, i);
}
// 添加广播发送记录，对调试有帮助
addBroadcastToHistoryLocked(r);
if (DEBUG_BROADCAST_LIGHT) Slog.v(TAG_BROADCAST, "Done with parallel broadcast ["
+ mQueueName + "] " + r);
}
......
do {
if (mOrderedBroadcasts.size() == 0) {
// No more broadcasts pending, so all done!
mService.scheduleAppGcsLocked();
if (looped) {
// If we had finished the last ordered broadcast, then
// make sure all processes have correct oom and sched
// adjustments.
mService.updateOomAdjLocked();
}
return;
}
r = mOrderedBroadcasts.get(0);
boolean forceReceive = false;
// Ensure that even if something goes awry with the timeout
// detection, we catch "hung" broadcasts here, discard them,
// and continue to make progress.
//
// This is only done if the system is ready so that PRE_BOOT_COMPLETED
// receivers don't get executed with timeouts. They're intended for
// one time heavy lifting after system upgrades and can take
// significant amounts of time.
int numReceivers = (r.receivers != null) ? r.receivers.size() : 0;
if (mService.mProcessesReady && r.dispatchTime > 0) {
long now = SystemClock.uptimeMillis();
if ((numReceivers > 0) &&
(now > r.dispatchTime + (2*mTimeoutPeriod*numReceivers))) {
Slog.w(TAG, "Hung broadcast ["
+ mQueueName + "] discarded after timeout failure:"
+ " now=" + now
+ " dispatchTime=" + r.dispatchTime
+ " startTime=" + r.receiverTime
+ " intent=" + r.intent
+ " numReceivers=" + numReceivers
+ " nextReceiver=" + r.nextReceiver
+ " state=" + r.state);
broadcastTimeoutLocked(false); // forcibly finish this broadcast
forceReceive = true;
r.state = BroadcastRecord.IDLE;
}
}
if (r.state != BroadcastRecord.IDLE) {
if (DEBUG_BROADCAST) Slog.d(TAG_BROADCAST,
"processNextBroadcast("
+ mQueueName + ") called when not idle (state="
+ r.state + ")");
return;
}
if (r.receivers == null || r.nextReceiver >= numReceivers
|| r.resultAbort || forceReceive) {
// No more receivers for this broadcast! Send the final
// result if requested...
// 广播发送完成，向广播发送者(广播接收机)返回结果
// r.resultAbort为true，表示某个接收机终止广播发送给后续接收机
if (r.resultTo != null) {
try {
if (DEBUG_BROADCAST) Slog.i(TAG_BROADCAST,
"Finishing broadcast [" + mQueueName + "] "
+ r.intent.getAction() + " app=" + r.callerApp);
performReceiveLocked(r.callerApp, r.resultTo,
new Intent(r.intent), r.resultCode,
r.resultData, r.resultExtras, false, false, r.userId);
// Set this to null so that the reference
// (local and remote) isn't kept in the mBroadcastHistory.
r.resultTo = null;
} catch (RemoteException e) {
r.resultTo = null;
Slog.w(TAG, "Failure ["
+ mQueueName + "] sending broadcast result of "
+ r.intent, e);
}
}
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST, "Cancelling BROADCAST_TIMEOUT_MSG");
// 一个广播向所有接收机发送完成，取消超时检测消息
cancelBroadcastTimeoutLocked();
if (DEBUG_BROADCAST_LIGHT) Slog.v(TAG_BROADCAST,
"Finished with ordered broadcast " + r);
// ... and on to the next...
添加到广播发送记录
addBroadcastToHistoryLocked(r);
if (r.intent.getComponent() == null && r.intent.getPackage() == null
&& (r.intent.getFlags()&Intent.FLAG_RECEIVER_REGISTERED_ONLY) == 0) {
// This was an implicit broadcast... let's record it for posterity.
mService.addBroadcastStatLocked(r.intent.getAction(), r.callerPackage,
r.manifestCount, r.manifestSkipCount, r.finishTime-r.dispatchTime);
}
// 删除已经发送完成的广播
mOrderedBroadcasts.remove(0);
r = null;
looped = true;
continue;
}
} while (r == null);
// Get the next receiver...
int recIdx = r.nextReceiver++;
// Keep track of when this receiver started, and make sure there
// is a timeout message pending to kill it if need be.
r.receiverTime = SystemClock.uptimeMillis();
if (recIdx == 0) {
// 广播发送给第一个接收机，记录分发时间
r.dispatchTime = r.receiverTime;
r.dispatchClockTime = System.currentTimeMillis();
if (DEBUG_BROADCAST_LIGHT) Slog.v(TAG_BROADCAST, "Processing ordered broadcast ["
+ mQueueName + "] " + r);
}
if (! mPendingBroadcastTimeoutMessage) {
// 如果没有检测广播超时消息，添加检测广播超时消息
long timeoutTime = r.receiverTime + mTimeoutPeriod;
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST,
"Submitting BROADCAST_TIMEOUT_MSG ["
+ mQueueName + "] for " + r + " at " + timeoutTime);
setBroadcastTimeoutLocked(timeoutTime);
}
......
if (nextReceiver instanceof BroadcastFilter) {
// Simple case: this is a registered receiver who gets
// a direct call.
// 动态注册的广播接收机
BroadcastFilter filter = (BroadcastFilter)nextReceiver;
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST,
"Delivering ordered ["
+ mQueueName + "] to registered "
+ filter + ": " + r);
deliverToRegisteredReceiverLocked(r, filter, r.ordered, recIdx);
if (r.receiver == null || !r.ordered) {
// The receiver has already finished, so schedule to
// process the next one.
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST, "Quick finishing ["
+ mQueueName + "]: ordered="
+ r.ordered + " receiver=" + r.receiver);
r.state = BroadcastRecord.IDLE;
scheduleBroadcastsLocked();
} else {
if (brOptions != null && brOptions.getTemporaryAppWhitelistDuration() > 0) {
scheduleTempWhitelistLocked(filter.owningUid,
brOptions.getTemporaryAppWhitelistDuration(), r);
}
}
return;
}
......
// 广播权限检查
int perm = mService.checkComponentPermission(info.activityInfo.permission,
r.callingPid, r.callingUid, info.activityInfo.applicationInfo.uid,
info.activityInfo.exported);
......
// 更新广播对于当前广播接收机的状态
r.delivery[recIdx] = BroadcastRecord.DELIVERY_DELIVERED;
r.state = BroadcastRecord.APP_RECEIVE;
r.curComponent = component;
r.curReceiver = info.activityInfo;
......
// 接收机的宿主进程已经运行
// Is this receiver's application already running?
if (app != null && app.thread != null) {
try {
app.addPackage(info.activityInfo.packageName,
info.activityInfo.applicationInfo.versionCode, mService.mProcessStats);
// 发送广播
processCurBroadcastLocked(r, app);
return;
......
}
......
}
// Not running -- get it started, to be executed when the app comes up.
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST,
"Need to start app ["
+ mQueueName + "] " + targetProcess + " for broadcast " + r);
// 广播接收机的宿主进程还没有运行，启动宿主进程
if ((r.curApp=mService.startProcessLocked(targetProcess,
info.activityInfo.applicationInfo, true,
r.intent.getFlags() | Intent.FLAG_FROM_BACKGROUND,
"broadcast", r.curComponent,
(r.intent.getFlags()&Intent.FLAG_RECEIVER_BOOT_UPGRADE) != 0, false, false))
== null) {
// Ah, this recipient is unavailable. Finish it if necessary,
// and mark the broadcast record as ready for the next.
Slog.w(TAG, "Unable to launch app "
+ info.activityInfo.applicationInfo.packageName + "/"
+ info.activityInfo.applicationInfo.uid + " for broadcast "
+ r.intent + ": process is bad");
logBroadcastReceiverDiscardLocked(r);
finishReceiverLocked(r, r.resultCode, r.resultData,
r.resultExtras, r.resultAbort, false);
scheduleBroadcastsLocked();
r.state = BroadcastRecord.IDLE;
return;
}
mPendingBroadcast = r;
mPendingBroadcastRecvIndex = recIdx;
}
}
对于动态注册的广播接收机，使用deliverToRegisteredReceiverLocked发送广播；对于静态注册的广播接收机，使用processCurBroadcastLocked发送广播。首先看deliverToRegisteredReceiverLocked。
private void deliverToRegisteredReceiverLocked(BroadcastRecord r,
BroadcastFilter filter, boolean ordered, int index) {
boolean skip = false;
// 检查是否为带有权限的广播接收机
if (filter.requiredPermission != null) {
int perm = mService.checkComponentPermission(filter.requiredPermission,
r.callingPid, r.callingUid, -1, true);
......
}
// 检查是否为带有权限的广播
if (!skip && r.requiredPermissions != null && r.requiredPermissions.length > 0) {
for (int i = 0; i < r.requiredPermissions.length; i++) {
String requiredPermission = r.requiredPermissions[i];
int perm = mService.checkComponentPermission(requiredPermission,
filter.receiverList.pid, filter.receiverList.uid, -1, true);
......
}
......
}
......
// 更新广播对于当前广播接收机的状态
r.delivery[index] = BroadcastRecord.DELIVERY_DELIVERED;
......
try {
if (DEBUG_BROADCAST_LIGHT) Slog.i(TAG_BROADCAST,
"Delivering to " + filter + " : " + r);
if (filter.receiverList.app != null && filter.receiverList.app.inFullBackup) {
// Skip delivery if full backup in progress
// If it's an ordered broadcast, we need to continue to the next receiver.
if (ordered) {
skipReceiverLocked(r);
}
} else {
// 发送广播
// r.resultData为前一个接收机传递给当前接收机的数据
performReceiveLocked(filter.receiverList.app, filter.receiverList.receiver,
new Intent(r.intent), r.resultCode, r.resultData,
r.resultExtras, r.ordered, r.initialSticky, r.userId);
}
if (ordered) {
r.state = BroadcastRecord.CALL_DONE_RECEIVE;
}
......
}
}
下面看performReceiveLocked
void performReceiveLocked(ProcessRecord app, IIntentReceiver receiver,
Intent intent, int resultCode, String data, Bundle extras,
boolean ordered, boolean sticky, int sendingUser) throws RemoteException {
// Send the intent to the receiver asynchronously using one-way binder calls.
if (app != null) {
if (app.thread != null) {
// If we have an app thread, do the call through that so it is
// correctly ordered with other one-way calls.
try {
// 通过one-way Binder IPC请求广播接收机运行
app.thread.scheduleRegisteredReceiver(receiver, intent, resultCode,
data, extras, ordered, sticky, sendingUser, app.repProcState);
// TODO: Uncomment this when (b/28322359) is fixed and we aren't getting
// DeadObjectException when the process isn't actually dead.
//} catch (DeadObjectException ex) {
// Failed to call into the process. It's dying so just let it die and move on.
// throw ex;
} catch (RemoteException ex) {
// Failed to call into the process. It's either dying or wedged. Kill it gently.
synchronized (mService) {
Slog.w(TAG, "Can't deliver broadcast to " + app.processName
+ " (pid " + app.pid + "). Crashing it.");
app.scheduleCrash("can't deliver broadcast");
}
throw ex;
}
} else {
// Application has died. Receiver doesn't exist.
throw new RemoteException("app.thread must not be null");
}
} else {
// 什么情况下，这样发送？
receiver.performReceive(intent, resultCode, data, extras, ordered,
sticky, sendingUser);
}
}
下面看静态注册的广播接收机的发送processCurBroadcastLocked
private final void processCurBroadcastLocked(BroadcastRecord r,
ProcessRecord app) throws RemoteException {
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST,
"Process cur broadcast " + r + " for app " + app);
if (app.thread == null) {
throw new RemoteException();
}
if (app.inFullBackup) {
skipReceiverLocked(r);
return;
}
r.receiver = app.thread.asBinder();
r.curApp = app;
app.curReceiver = r;
app.forceProcessStateUpTo(ActivityManager.PROCESS_STATE_RECEIVER);
mService.updateLruProcessLocked(app, false, null);
mService.updateOomAdjLocked();
// Tell the application to launch this receiver.
// 通过Binder IPC通知应用运行的组件信息
r.intent.setComponent(r.curComponent);
boolean started = false;
try {
if (DEBUG_BROADCAST_LIGHT) Slog.v(TAG_BROADCAST,
"Delivering to component " + r.curComponent
+ ": " + r);
mService.notifyPackageUse(r.intent.getComponent().getPackageName(),
PackageManager.NOTIFY_PACKAGE_USE_BROADCAST_RECEIVER);
// 通过one-way Binder IPC请求广播接收机运行
app.thread.scheduleReceiver(new Intent(r.intent), r.curReceiver,
mService.compatibilityInfoForPackageLocked(r.curReceiver.applicationInfo),
r.resultCode, r.resultData, r.resultExtras, r.ordered, r.userId,
app.repProcState);
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST,
"Process cur broadcast " + r + " DELIVERED for app " + app);
started = true;
} finally {
if (!started) {
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST,
"Process cur broadcast " + r + ": NOT STARTED!");
r.receiver = null;
r.curApp = null;
app.curReceiver = null;
}
}
}
广播接收机处理有序广播的流程分析
以动态注册的广播接收机为例，通常调用ActivityThread的scheduleRegisteredReceiver接收广播。
下面从scheduleRegisteredReceiver开始分析。
public void scheduleRegisteredReceiver(IIntentReceiver receiver, Intent intent,
int resultCode, String dataStr, Bundle extras, boolean ordered,
boolean sticky, int sendingUser, int processState) throws RemoteException {
updateProcessState(processState, false);
// 这里的receiver是InnerReceiver对象，也就是IIntentReceiver.Stub对象
receiver.performReceive(intent, resultCode, dataStr, extras, ordered,
sticky, sendingUser);
}
下面看InnerReceiver的performReceive方法
public void performReceive(Intent intent, int resultCode, String data,
Bundle extras, boolean ordered, boolean sticky, int sendingUser) {
// resultCode、data、extras为前一个广播接收机传递给当前接收机的数据
final LoadedApk.ReceiverDispatcher rd;
if (intent == null) {
Log.wtf(TAG, "Null intent received");
rd = null;
} else {
rd = mDispatcher.get();
}
if (ActivityThread.DEBUG_BROADCAST) {
int seq = intent.getIntExtra("seq", -1);
Slog.i(ActivityThread.TAG, "Receiving broadcast " + intent.getAction()
+ " seq=" + seq + " to " + (rd != null ? rd.mReceiver : null));
}
if (rd != null) {
// 调用ReceiverDispathcer的performReceive
rd.performReceive(intent, resultCode, data, extras,
ordered, sticky, sendingUser);
} else {
......
}
}
下面分析ReceiverDispathcer的performReceive
public void performReceive(Intent intent, int resultCode, String data,
Bundle extras, boolean ordered, boolean sticky, int sendingUser) {
final Args args = new Args(intent, resultCode, data, extras, ordered,
sticky, sendingUser);
if (intent == null) {
Log.wtf(TAG, "Null intent received");
} else {
if (ActivityThread.DEBUG_BROADCAST) {
int seq = intent.getIntExtra("seq", -1);
Slog.i(ActivityThread.TAG, "Enqueueing broadcast " + intent.getAction()
+ " seq=" + seq + " to " + mReceiver);
}
}
// 向mActivityThread绑定的线程中post广播消息
if (intent == null || !mActivityThread.post(args)) {
if (mRegistered && ordered) {
IActivityManager mgr = ActivityManagerNative.getDefault();
if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG,
"Finishing sync broadcast to " + mReceiver);
args.sendFinished(mgr);
}
}
}
下面分析Args的run方法
public void run() {
final BroadcastReceiver receiver = mReceiver;
final boolean ordered = mOrdered;
......
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "broadcastReceiveReg");
try {
ClassLoader cl = mReceiver.getClass().getClassLoader();
intent.setExtrasClassLoader(cl);
intent.prepareToEnterProcess();
setExtrasClassLoader(cl);
receiver.setPendingResult(this);
// 执行接收机的onReceive方法
receiver.onReceive(mContext, intent);
} catch (Exception e) {
if (mRegistered && ordered) {
if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG,
"Finishing failed broadcast to " + mReceiver);
sendFinished(mgr);
}
if (mInstrumentation == null ||
!mInstrumentation.onException(mReceiver, e)) {
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
throw new RuntimeException(
"Error receiving broadcast " + intent
+ " in " + mReceiver, e);
}
}
if (receiver.getPendingResult() != null) {
// 通知AMS广播处理完成
finish();
}
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
}
下面分析finish实现
public final void finish() {
if (mType == TYPE_COMPONENT) {
// 当前的广播接收机为静态注册
final IActivityManager mgr = ActivityManagerNative.getDefault();
if (QueuedWork.hasPendingWork()) {
// If this is a broadcast component, we need to make sure any
// queued work is complete before telling AM we are done, so
// we don't have our process killed before that. We now know
// there is pending work; put another piece of work at the end
// of the list to finish the broadcast, so we don't block this
// thread (which may be the main thread) to have it finished.
//
// Note that we don't need to use QueuedWork.add() with the
// runnable, since we know the AM is waiting for us until the
// executor gets to it.
QueuedWork.singleThreadExecutor().execute( new Runnable() {
@Override public void run() {
if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG,
"Finishing broadcast after work to component " + mToken);
sendFinished(mgr);
}
});
} else {
if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG,
"Finishing broadcast to component " + mToken);
sendFinished(mgr);
}
} else if (mOrderedHint && mType != TYPE_UNREGISTERED) {
// 动态注册的广播接收机接收有序广播
if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG,
"Finishing broadcast to " + mToken);
final IActivityManager mgr = ActivityManagerNative.getDefault();
sendFinished(mgr);
}
}
下面看sendFinished
public void sendFinished(IActivityManager am) {
synchronized (this) {
if (mFinished) {
throw new IllegalStateException("Broadcast already finished");
}
mFinished = true;
try {
if (mResultExtras != null) {
mResultExtras.setAllowFds(false);
}
if (mOrderedHint) {
// 有序广播，通知AMS广播处理完成
// mResultCode、mResultData、mResultExtras为当前广播接收机传递给下一个广播接收机的result
am.finishReceiver(mToken, mResultCode, mResultData, mResultExtras,
mAbortBroadcast, mFlags);
} else {
// This broadcast was sent to a component; it is not ordered,
// but we still need to tell the activity manager we are done.
am.finishReceiver(mToken, 0, null, null, false, mFlags);
}
} catch (RemoteException ex) {
}
}
}
最后看一下AMS的finishReceiver
public void finishReceiver(IBinder who, int resultCode, String resultData,
Bundle resultExtras, boolean resultAbort, int flags) {
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST, "Finish receiver: " + who);
// Refuse possible leaked file descriptors
if (resultExtras != null && resultExtras.hasFileDescriptors()) {
throw new IllegalArgumentException("File descriptors passed in Bundle");
}
final long origId = Binder.clearCallingIdentity();
try {
boolean doNext = false;
BroadcastRecord r;
synchronized(this) {
BroadcastQueue queue = (flags & Intent.FLAG_RECEIVER_FOREGROUND) != 0
? mFgBroadcastQueue : mBgBroadcastQueue;
// 当前正在发送的广播
r = queue.getMatchingOrderedReceiver(who);
if (r != null) {
// 完成广播对于之前广播接收机的发送
doNext = r.queue.finishReceiverLocked(r, resultCode,
resultData, resultExtras, resultAbort, true);
}
}
if (doNext) {
// 准备发送给下一个广播接收机
r.queue.processNextBroadcast(false);
}
trimApplications();
} finally {
Binder.restoreCallingIdentity(origId);
}
}
小结
Q&A
- 广播超时，是针对一个广播的单个接收机还是所有的接收机？单个
- 如果一个广播接收机刚收到串行广播，就被杀死了，会不会产生广播ANR? 不会
